1. Field of the Invention
The field of the invention is earth boring bits-especially the seal and lubrication systems for rolling cutter rock bits.
2. Description of the Prior Art
Recently, metal face seals have been used successfully to seal lubricant within the rotatable cutters and around the cantilevered bearing shaft of a rock bit. U.S. Pat. No. 4,516,641, "Earth Boring Bit With Pressure Compensating Rigid Face Seal," May 14, 1985, to Burr, includes background information leading to this milestone in the ongoing search for rock bit seal improvement. The seal disclosed in U.S. Pat. No. 4,516,641 utilizes two rigid rings that are urged against one another by a pair of elastomeric rings confined in a seal groove between each cutter and its supporting bearing shaft. Because the axial seal movement is greater than the axial cutter movement, a grooved geometry is provided to permit relatively unrestricted seal assembly movement. As a result, pressure pulses in the lubricant around the seal and associated lubricant losses are minimized. The seal assembly thus becomes a supplemental pressure compensator that assists the primary compensator in each leg of the bit in maintaining a selected low pressure differential across the seal assembly.
An improvement to the structure disclosed in U.S. Pat. No. 4,516,641 is disclosed in U.S. Pat. No. 4,666,001, "Earth Boring Bit With Improved Rigid Face Seal Assembly," May 19, 1987, to Burr. If the rigid rings are positioned in a groove inside the periphery of an associated journal bearing surface, axial seal movement may be decreased relative to axial cutter movement. In the preferred embodiment, the axial seal movement is one half that of the cutter, which better balances the load applied to each half of the seal assembly. Hence, prolonged life of the seal assembly may be expected. An improvement to the structure disclosed in U.S. Pat. No. 4,666,001 is disclosed in U.S. Pat. No. 4,753,304, "Volume And Pressure Balanced Rigid Face Seal For Rock Bit," Jun. 28, 1988, to Burr. That structure provides a the ratio of axial seal movement to axial cutter movement of one to one, thereby eliminating the rigid ring and energizer associated with the cutter. Furthermore, groove and seal geometry are further refined to prevent lubricant loss due to a sudden pressure differential across the seal.
U.S. Pat. No. 4,923,020, "Rock Bit With Rigid Face Seals And Recessed Energizers," May 8, 1990, discloses a return to the two rigid ring, two energizer technology. The structure disclosed employs the geometry refinements disclosed in U.S. Pat. No. 4,753,304 and further provides refined seal and groove geometry adapted to the two rigid ring, two energizer technology.